Diamond

Diamond is a generic building material that is only obtainable in the Oil Biome, where it is present in moderately limited quantity.

A Duplicant must learn the Superduperhard Digging Skill to excavate Diamond.

Usage
Only Tempshift Plates, Window Tiles and Aero Pots can be built from Diamond (plus the Monument Top, where Diamond is one of the required materials). Its high Thermal Conductivity and melting temperature make it one of the best materials for Tempshift Plates. When building Window Tiles and Aero Pots, its decor modifier of +100% is relevant.

It also increases overheat temperature by 200 C. However, none of the buildings it can be used for have an overheat temperature, so this quality has no in-game effect.

Radiant Bugs can eat Diamond, and it can be used in Airborne Critter Bait to attract Radiant Bugs.

Mods
There is a mod that enables using Diamond for constructions, see here.

Trivia
Although not all thermal conductivity values in the game represent the real life values, diamond is notable, as its thermal conductivity in real life would be 2200 DTU/(m*s) / °C (natural diamond), more than 27 times the in-game value.